1. Field of the Invention
The invention relates in general to a cable reel, and more particularly to an intermediate or storage reel for temporarily receiving a variable cable length between a stationary end and a movable end of the cable. The term "cable" as used herein and in the accompanying claims means an electric conductor, a hydraulic or pneumatic line and also hybrid combinations thereof.
2. Discussion of the Prior Art
With reels that are arranged between a stationary apparatus, e.g., a measuring or control station on one end and a movable apparatus, for instance a measuring probe or a remote control apparatus on the other end, twisting of the cable during rotation of the reel is a frequent problem which is desirable to avoid.
In the case of hydraulic lines, a rotary fluid clutch is frequently used with a stationary portion and a second portion rotatable relative thereto, with suitable seals being disposed between the two portions. The stationary portion of so-called Rotary Seals or Swivels is connected to stationary apparatus, e.g., a fluid source, while the rotary portion thereof is connected to the reel. Analogous constructions are also known for pneumatic lines and for fibre optic cables. In electrical conductors, slip ring connections are frequently used wherein for each conductor a carbon brush is connected to the non-rotary apparatus, e.g., a measuring station for the portal of a mobile crane, and for each conductor a slip ring is mounted in co-rotational relationship with the reel. The prior art aids described above are sufficient with a limited or small number of fluid lines or conductors per cable. Furthermore, a plug connection may also be used which is released during reel rotations. However, this may present problems if a specific fluid pressure or electrical voltage must be maintained constantly in the cable.
However, substantial problems are encountered with more complex cables, such as cables that are composed of a plurality of fluid lines or electric conductors or combinations thereof. For instance, in mobile transport installations it is generally necessary not only to supply continuous electric power, but often other electric connections must also be maintained continuously for control, locking, communication, measurement of lifted weights or of transported quantities and the like. Practical constructional problems not only impose a restriction on the possible number of slip rings, but also these electric connections are often unreliable because of variations in the transitional resistance across the slip ring connections. Also, another example is found in seismic operations at sea wherein use may be made of a measuring probe maintained a variable distance from a ship by means of a float. In these arrangements a cable comprising many electric conductors and/or hydraulic lines is enclosed by a jacket, and is coupled to a computer on the ship. The length of this cable should be frequently changed, for instance for adaptation to local conditions or for maintenance operations on the measuring probe. To prevent twisting, which is unallowable for such cables, prior art aids, such as the above-mentioned rotary clutches or slip ring contacts are not adequate, partially because contaminated slip rings have an excessive adverse effect upon the inetlligence signals which have a magnitude in millivolts. In view thereof, it has been necessary heretofore, during retrieval of the measuring probe to arrange the cable on the deck in some fashion in loops or to suspend the same. Since this operation has to be accomplished very carefully, the retrieval and letting out of a measuring probe is a time-consuming operation, and often takes several hours.